The laboratory report is divided in two sessions: Pre-Lab to be prepared before the lab, and Post-Lab to be prepared after the experiment. Both have to be uploaded in turnitin.com, as a MS-Word file. You can upload the fine only once, and you cannot resubmit.
You have to use the following template files
Class turnitin.com Class ID: 16298199
It must contain:
1. One paragraph describing procedure of the experiment.
2. The answers of the "pre-lab" questions of the given experiment, see lab-manual.
Introduction (2 paragraphs)
The purpose of this experiment is to determine the molar heat of vaporization of water ( Δ Hvap) using the Clausius-Clapeyron equation:a (Chapter 11, Brown and LeMay) b
where P is the vapor pressure of water and T is the temperature of the water in Kelvin, R is a the gas constant (8.314 J/mol K) and A is a constant. The Clausius-Clapeyron equation exhibits a relationship between the natural log of the vapor pressure (ln P) of a liquid and the reciprocal of the temperature (1/T) such that by plotting ln P (y-axis) vs 1/T (x-axis) a straight line occurs with a slope =-Δ Hvap/RT. In other words, the Clausius-Clapeyron equation is in the form of a straight line (y = mx + b)c.
A liquid boils when its vapor pressure matches the prevailing atmospheric pressure so as atmospheric pressure decreases so does the temperature at which the liquid boils. This experiment will reduce the apparent atmospheric pressure in a closed flask of water and measure the boiling temperatures of the water under these different conditions of apparent atmospheric pressuredd.
A set of corresponding vapor pressure and temperature values will be collected for the water under these conditions. The collected set of vapor pressure/temperature data are then plottede in order to find the slope of the straight line so that theΔ Hvap can be calculated:
Δ Hvap = - (slope)(R)
The literature value listed for the molar heat of vaporization of water is
Δ Hvap = 40.67 kJ/mol f.
Results (2 paragraph)
This section should contain the tear-out data sheets from the lab text and any Excel graphs generated
Calculations (1 paragraph)
This section should contain all calculations necessary to obtain the experimental results from the experimental data and should be on the tear-out data sheets. Extra pages may be included for calculations if there is not enough room on the tear-out sheets.
Discussion (2 paragraphs)
The Clausius-Clapeyron equation gives the relationship between the vapor pressure and temperature of a liquida:
Given that a liquid boils when its vapor pressure is equal to the atmospheric pressure, we were able to acquireb vapor pressure data at different temperatures by reducing the pressure inside a flask of water and gradually heating the water to determine its vapor pressure and respective boiling temperature under conditions of lower apparent atmospheric pressure. The plot of lnP vs 1/T produced a nearly straight line with a linear best-fit shown by the equation y = - 4635.1x + 18.985 and a correlation coefficient of R2 = 0.9989 (1.000 is a perfect fit). The correlation coefficient indicatesc that the data points fit the straight best-fit line quite well. The slope of the line (slope = - 4635.1 K) is related to the molar heat of vaporization of water:
Δ Hvap = - (slope)(R)
The calculated value of Δ Hvap = 38.5 kJ/mold was determined from the slope of the plotted data. The literature value is Δ Hvap = 40.67 kJ/mol and the error is 5.24%e. It should be noted that the result for the calculated molar heat of vaporization is only as good as the slope of the best straight-line fit of the data. In addition, the calibration of the thermister and the pressure sensors is extremely important in the collection of accurate data. If the calibration of either (or both) of the units is incorrect, a small variation in slope can greatly affect the calculated valuef (a slope of – 3635 K instead of – 4635 K would produce a Δ Hvap = 30.2 kJ/mol, over 10 kJ/mol lower that the literature value!).
a The purpose and concept used is clearly stated. Note that the text book is referenced as being a source of information
b Any mathematical equations or chemical equations that describe the experiment should be clearly given—not in a text line, but on a separate line—with symbols defined
c The relationship between the purpose (finding DHwap) and the mathematical relationship (Clausius-Clapeyron equation) is explained.
d A very brief and conceptual description of how the data is to be obtained may be necessary, but any specific experimental procedure should not be given in the introduction.
e Note the use of more formal language here “data are plotted” rather than “we plotted the data”.
f If there are known or literature values for the expected results, they should be given
Note: the spacing is 1.5 lines to allow for easier reading, comments and corrections.
Make sure all data is given in the correct number of significant digits and has the appropriate units!!.
Calculations should be organized and written neatly, showing all units.
a A brief review of the concepts is appropriate, showing any mathematical or chemical equations that are important.
b Note the use of first person; for our purposes, the R&D can be written a little more informally than the introduction, which should be written in third person.
d The slope is given with the final experimental result as well as the mathematical relationship.
e Since a literature value is known, an experimental error can be calculated.
f There should be a brief discussion of what could cause error in the experiment—and this is not ”I misread the balance”! This should be error that can occur from conditions in the collection of data and the processing of the data.